The major histocompatibility complex (MHC) of mammals plays a pivotal role in antigen-specific regulation of the immune response of thymus-derived (T) lymphocytes. In fact, the MHC has been implicated in regulating susceptibility to a variety of disease states including diabetes melitus and multiple sclerosis. Therefore, the critical evaluation of the organization and structure of Class I and Class II MHC genes and the immunological function of their cell-surface products is of paramount importance. The laboratory rat has provided an excellent model for a number of human disease states; this fact emphasizes the urgency for a comprehensive, genetic and functional analysis of the rat MHC, RT1. The research program proposed in this application comprises such a comprehensive analysis. The primary objective of this program is the cloning of individual RT1 Class I and Class II genes followed by the characterization of their gene products at the molecular and functional levels in isolation in mouse cells after DNA-mediated gene transfer. The minimum number and polymorphism of RT1 Class I and Class II sequences will be obtained with genomic blots of digested DNA derived from a panel of inbred strains, intra-RT1 recombinant strains, wild rat-derived congenic strains, and captured wild rats. Class I and Class II sequences will be cloned from Lambda genomic libraries; cloned genes will be characterized by (1) restriction site mapping, (2) nucleotide sequencing, and (3) intra-RT1 mapping. Cloned Class I and Class II sequences will be transferred to mouse tissue culture cells by DNA-mediated gene transfer; expressed RT1 gene products will be characterized by serology, two-dimensional gel electrophoresis, and T cell- mediated assays. The ability of Class I and Class II gene products to present foreign antigens to cytotoxic and IL-2-secreting T cells, respectively, will be investigated. Specifically, Class II gene products will be tested, in collaboration, for their ability to present myelin basic protein to rat IL-2-secreting T cells with the aim of identifying the functional Class II gene(s) and the domain of its product involved in presentation of antigen in the experimental allergic encephalitis syndrome. The proposed experiments are expected to assign specific molecular characteristics and immunological functions of RT1 genes to individual genes.